I have 3 OS now. I only want 2!

How do I get rid of one of them and which one?
I have RH Linux 2.4.18-17.7.x (or something like that)
I have RH Linux 2.4.18.3
And I have DOS
I know I want DOS so which Red Hat is the older one? I think 2.4.18-17.7.x is
but I best ask the experts on list before I do anything. I also need to know
how to do it and how I take DOS off for when I want to not have it.
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:-)~Mike~(-: